The present invention relates to a speed-increased small powered boat such as racing boats, high-speed fisherboats, motorboats for sportfishing and the like. More particularly, the invention relates to a means to increase the speed of a small powered boat, which proceeds at such a high speed that the waterline of the boat body varies depending on the speed of the boat, by suppressing the wave-making resistance.
Needless to say, any ships or boats proceeding afloat on the surface of water produce waves so that a major portion of the energy output of the engine is lost against the wave-making resistance so that the maximum speed of the vessel is limited thereby since the wave-making resistance is rapidly increased as the speed of the vessel is increased.
The wave-making resistance here implied is the resistance caused by a gravity wave produced as a result of proceeding of a vessel afloat. The most important factor affecting the wave-making resistance is the so-called Froude number which is a hydrodynamical parameter as the ratio of the force of inertia and the gravity.
Accordingly, it is natural that the wave-making resistance could be decreased when the gravity of the vessel per se is decreased. In this regard, various attempts and proposals have been made in the prior art. For example, a proposal is made in Japanese Patent Publications 55-15349 and 48-35557, according to which the ship hull is provided with a large number of air-jet openings or holes on or near the ship bottom and compressed air is ejected therefrom into the water to form bubbles therein so that the ship body receives an increased buoyant force.
Setting aside submarine boats having no free surface which proceed with the body entirely submerged, this method of bubble formation in water has no effect to decrease the wave-making resistance without reducing occurrence of waves due to proceeding of the ship afloat on the water surface. Moreover, the ship running on the mass of bubbles is under a risk of eventual capsizing when the speed thereof exceeds a certain upper limit. Therefore, this method of air-jet bubbling is not practical if not to mention the cost therefor.
Alternatively, Japanese Patent Kokai 60-33185 proposes a method in which compressed air is ejected into the water in front of the proceeding ship to produce a water mass containing numberless bubbles by which the ship receives a decreased resistance from water. This method is also not practical because of the great investment for the air compressor and other accessories for ejecting compressed air as well as the very large energy consumption for the ejection of the compressed air against water pressure.
The inventors have previously proposed, in U.S. Pat. No. 5,088,433, a simple but very efficient means to suppress the wave-making resistance on a ship body proceeding afloat. Namely, the wave-making resistance on a proceeding ship can be greatly decreased by providing the ship hull with at least one pair of fins mounted on the hull surface at symmetrical positions each extending above and below the waterline, each fin being fixed to the ship hull at the front end line thereof without leaving a gap opening therebetween and the rear end of the fin outwardly extending to make a specified fin-mounting angle with the hull surface.
This means is indeed very effective when the fins are installed on the ship hull of a relatively large vessel of which the depth of the waterline little depends on the speed of the vessel. When this means is applied to a relatively small powered boat of high speed such as racing boats, however, the effect of wave-making resistance suppression is not always quite satisfactory since the depth and direction of the waterline are greatly changed depending on the speed of the boat.